Patent GB-1122423-A (GB)
Title: Improvements in or relating to glass manufacturing processes and apparatus
IPC: G05D9/12
Filed: 1964-12-18
Abstract: <PICT:1122423/C1/1> In a glass manufacturing process the surface level of a body of molten glass is continuously indicated by drawing a bead of glass from the surface of the molten glass, measuring the resistance of an electrical circuit including that bead, detecting any change in resistance of the circuit from a resistance value corresponding to a predetermined height of the bead, producing a signal indicative of that change of resistance, employing the signal to return the height of the drawn bead of molten glass to said predetermined height, and monitoring said signal to obtain a continuous indication of the surface level of the molten glass.  The surface level measuring device comprises a carbon electrode 44 (Fig. 2) mounted beneath an insulated crosspiece 46 attached by a piston-rod 50 to a watercooled pneumatic-positioning device 51. The electrode 44 preferably passes through a hole in the roof of a small pocket in the side wall of a glass-melting furnace.  The tip of the electrode is covered with platinum or a platinum/rhodium alloy.  The electrode is dipped into the glass and withdrawn to form a bead 59 from 1/16 to 1/8 inch high, the position being determined by a manual adjustment device 55 attached to apparatus 51. This sets the datum level for the glass. Another electrode 60 permanently immersed in the molten glass is fixed to a side wall of the pocket. Both electrodes are connected to a bridge 65 (see Fig. 3, not shown) which is initially balanced when the bead is drawn to predetermined height, e.g. 3/32 inch.  The bridge is connected to an amplifier 69 in turn connected to a servomotor 71 which drives the wiper 73 of a variable resistance 74 in a constant voltage circuit.  The arm 73 is in turn connected to a current to pressure converter 77 which translates the electrical signal from the bridge 65 into a pneumatic signal, which is fed through a pressure comparator device 130, 142 (Fig. 7, not shown) to operate the positioning device 51.  When the glass level varies it alters the height of the bead 59, the resistance of which changes upsetting the balance of the bridge 65.  This sends out an error signal which is translated into a pneumatic signal, changes in which are noted in the comparator device 130, 142, thus causing movement of the positioning device 51 to move the electrode 44 to restore the bead 59 to its predetermined height and thus rebalance the bridge 65. The same pneumatic signal from the converter 77 operates a recorder controller device 33 (Fig. 4) which sets down a visible indication of the glass level with reference to the datum line from the movement of the electrode 44.  At the same time the control part of device 33 sends back a signal to the glass feeder mechanism to either increase or decrease the rate of feed to the furnace.  The feeding means may be a rotating roller having longitudinal vanes extending radially therefrom which feeds batch into the furnace at a rate commensurate with its speed of rotation, or in a fibre glass furnace may be either a means for altering the rate of feed of marbles to the furnace or a variable atmospheric pressure above a bead of glass in a feeder compartment, or may be a vertically adjustable tweel in a feeder canal of a vertical sheet drawing apparatus.